<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>灯泡</title>
</head>
<body>
    <img id="h1" src="./img/off.gif">  <br><br>
    <div class="cls">杰普软件</div>   <br>
    <div class="cls">Java程序员</div>  <br>
    <input type="checkbox" name="hobby"> 电影
   <input type="checkbox" name="hobby"> 旅游
   <input type="checkbox" name="hobby"> 游戏
</body>
<script>
     //1. 点亮灯泡 : src 属性值
//首先获取img标签对象
var img = document.getElementById('h1');
 //然后修改img标签对象的src属性值，进行图片的切换
img.src = "./img/on.gif";
 //2. 将所有div标签的内容后面加上: very good (红色字体) -- 
//  <font color='red'> 
//     </font> 
var divs = document.getElementsByTagName('div');
 for (let i = 0; i < divs.length; i++) {
 const div = divs[i];
 div.innerHTML += " <font color='red'>very good</font>"; 
}
 // //3. 使所有的复选框呈现选中状态
var ins = document.getElementsByName('hobby');
 for (let i = 0; i < ins.length; i++) {
 const check = ins[i];
 check.checked = true;//选中
}
</script>
</html>